1. FIELD OF THE INVENTION
The present invention relates generally to internal combustion engines and, more particularly, to an engine which utilizes a piston having two diameters that define a step therebetween which is disposed in a cylinder with two diameters.
2. DESCRIPTION OF THE PRIOR ART
Many different types of internal combustion engines are well known to those skilled in the art. One particular type of engine is a two cycle engine. A common problem that occurs with two cycle engines is that, at low speeds, unburned fuel can be emitted in the exhaust stream. Naturally it is not desirable to exhaust hydrocarbons, in the form of unburned fuel, into the atmosphere for ecological reasons.
The emission of fuel in the exhaust stream can be caused at low speeds by the fact that a fuel/air mixture enters the combustion chamber prior to the exhaust port being closed. Under certain circumstances, the fuel/air mixture can propagate through the combustion chamber and pass out the exhaust port prior to the ignition of the fuel within the combustion chamber.
In certain applications of two cycle engines, fuel injection is used to alleviate this problem. Fuel injectors can be disposed in fluid communication with the combustion chamber, either through a cylinder wall or through the end of the cylinder. One of the goals of these types of solutions is to provide a stratified charge of fuel at one portion of the combustion chamber a distance away from the exhaust port.
U.S. Pat. No. 4,068,629, which issued to Hooper on Jan. 17, 1978, discloses a stepped piston two stroke engine which includes at least two cylinders. Each cylinder has a working part of smaller diameter and a pumping part of larger diameter. The main inlet ports are arranged symmetrically about and spaced from a plane which contains a longitudinal access of the cylinder and which passes through the center of the exhaust port. The auxiliary inlet port is provided in the cylinder wall opposite the exhaust port. Main and auxiliary transfer passages are provided for the main and auxiliary inlet ports. The auxiliary inlet ports and auxiliary transfer passages lie wholly on one side of an axial plane which contains the axes of the two cylinders of the set. The exhaust ports of both cylinders on the other side of this plane. Only air may be supplied to the working part of each cylinder through the main inlet ports, while fuel is injected into the air passing through the auxiliary transfer passages so that a mixture of fuel and air enters the working parts of the cylinders through the auxiliary inlet ports. By this means charge stratification in the working parts of the cylinders can be achieved.
U.S. Pat. No. 4,138,971, which issued to Fujikawa et al on Feb. 13, 1939, describes a crank chamber precompression type two-cycle internal combustion engine which includes a pair of stepped cylinders and a pair of stepped pistons slidably disposed in the cylinders. These define annular spaces of variable volume in the cylinders. The pistons are interconnected to each other with 180 degrees phase difference. An air-fuel mixture is introduced into the annular space in one cylinder and forced into the crank chamber of the other cylinder during the upward stroke of the associated piston, so that an additional charge is provided.
U.S. Pat. No. 4,169,434, which issued to Guenther on Oct. 2, 1979, describes an internal combustion engine with a stepped piston supercharger. A reciprocating piston four cycle internal combustion engine utilizes a stepped piston. The stepped portion of the piston works in an enlarged bore in the block of the engine, and serves as a compressor to provide a supercharged fuel-air mixture into the combustion chamber. The compressor delivers two compression strokes per engine cycle. The compressed fuel-air mixture travels from the compressor via a bypass manifold which also serves as an accumulator. It then passes to the main cylinder via an intake valve. The fuel-air mixture is admitted to the compressor cylinder through the crankcase and valved passages through the stepped portion of the piston.
U.S. Pat. No. 4,210,108, which issued to Hooper on Jul. 1, 1980, discloses a stepped piston two stroke engine which has a stepped piston in which the cylinder casting has a bore of greater diameter to form a pumping part, a bore of lesser diameter to form a working part, exhaust port means in the working part and opposed transfer part means on opposite sides of the working part disposed symmetrically about a plane passing through the longitudinal axis of the cylinder. The plane also passes through the center of the exhaust port means. The transfer port means is of a form to be produced in the casting process by non-separate cores introduced lineally towards the plane.
U.S. Pat. No. 4,522,163, which issued to Hooper on Jun. 11, 1985, describes a stepped piston and a stepped piston engine. The engine has one or more cylinders and each cylinder contains a stepped piston having a pumping part of larger diameter and a working part of smaller diameter. The working part of the piston is slidably in and associated with a working part of the cylinder in which a combustion of a fuel-air mixture takes place. The pumping part of the piston is slidably in and associated with a pumping part of the cylinder. The piston has a body with an interial hollow opening to the outside toward the lower end of the piston. The body comprises a smaller diameter working part which extends from the top of the piston to a step and a larger diameter pumping part extending from the step to a lower end of the piston. At least one piston ring groove is formed in an outer surface of the smaller diameter part and at least one piston ring groove is formed in the outer surface of the large diameter part.
U.S. Pat. No. 5,189,995, which issued to Hooper on Mar. 2, 1983, describes a stepped piston engine that comprises first, second and third step cylinders with each cylinder having a large diameter pumping part and a small diameter working part. A piston is slidable in the cylinder and each piston is coupled to an output shaft of the engine. A first transfer passage transfers the precompressed charge from the large diameter pumping part of the first cylinder to the smaller diameter pumping part of the second cylinder. A second transfer passage transfers precompressed charge from the large pumping part of the second cylinder to the smaller diameter working part of the third cylinder. A third transfer passage transfers precompressed charge from the large diameter pumping part of the third cylinder to the smaller diameter working part of the first cylinder.
One of the many designs for pistons for internal combustion engines is described in an article titled "Hooper's Hope" which was written by Dave Searle and Doug Jackson in the Oct., 1996 issue of Motorcycle Consumer News. This article describes a piston which comprises two portions, one with a diameter that is less than the other. The configuration, because of its physical appearance, is sometimes referred to as "Top Hat" piston. The configuration described in this article utilizes two cylinders, as a cooperative pair, with one cylinder providing an air flow into the combustion chamber of the other cylinder. The design described in this reference requires cylinders to be arranged in such a way that they are able to cooperate with each other in an associated pair.
It would therefore be significantly beneficial if a two cycle engine could be developed which is able to provide a stratified charge into the combustion chamber of the cylinder without the need for complex fuel injection systems.